Heating of glass sheets in a gas-fired forced convection furnace has been known in the art for several years. Indeed, one such type of prior art gas-fired furnace conveys a sheet of glass through the furnace on a bed of air. As the glass "floats" through the furnace, hot air is distributed toward and into contact with the top and bottom surfaces of the glass sheet. However, due to the complexity of a "floating" system, prior art devices of this type typically use convective heat flow to the bottom surface of the glass sheet, and radiant heat flow to the top surface of the glass sheet.
After the heated working fluid has impinged the bottom surface of the glass sheet, a portion of the "spent" working fluid is randomly returned toward a proximally positioned gas burner where the spent working fluid and newly produced products of combustion are mixed and then recirculated toward impingement of same on the glass sheet.
Furthermore, prior art gas-fired heating devices have also been used in which convective heat that is to impinge upon the top surface of a glass sheet is distributed from one or more gas burners located above the glass sheet as it passes through the device, and, convective heat that impinges the bottom surface of the glass sheet is distributed by one or more gas burners located below the glass sheet.
However, existing gas-fired convection heating systems cannot provide the capability of separately controlling the velocity of impingement of the working fluid with the surface of the glass sheet to be heated, independent from control of the heat input to the system.
In addition, none of such prior art devices disclose, much less suggests, the use of gas-fired burners operably positioned above and below the glass sheet for producing and, in turn, distributing, forced convective flow of the hot working fluid to corresponding ones of the top and bottom surfaces of the glass sheet in which: (1) the heat input to and, consequently, the temperature of, the working fluid above and below the glass sheet may be controlled independently; and/or (2) the impingement velocity of the hot working fluid being distributed onto the top and bottom surfaces of the glass sheet can be independently controlled--toward uniform control of convection heat transfer to the top and bottom surfaces of the glass sheet, to, in turn, compensate for glass thickness, coating and color, among other variables.
And, although such prior art devices have indeed disclosed recirculation of spent working fluid and use of gas-fired burners, none of such prior art devices disclose, much less suggests, drawing spent hot working fluid toward and into a mixing chamber operably and closely positioned about a substantial portion of a gas burner--in which the gas burner is specifically intended to produce, for distribution, hot combustion gases to the respective top and/or bottom surfaces of the glass sheet being heated.
These and other features of the present invention will become apparent because of the present specification, claims and drawings.